Project Summary Rapidly accumulating evidence suggests that modifying gut microbiota may promote health or treat disease, with fecal microbiota transplantation (FMT) for C. difficile infection (CDI) being the first successful clinical application of this concept. Given the rising incidence of CDI and the lack of effective therapies for recurrent CDI, the use of FMT is growing rapidly, despite a paucity of clinical data and despite the theoretical risk that transfer of gut microbiota may induce chronic diseases. The early adoption and expansion of FMT in clinical practice has bypassed the standard investigatory pathway and preceded large randomized controlled trials that typically evaluate efficacy and contribute important short- and long-term safety data. In order to overcome this deficit in knowledge and experience, we propose to develop a national FMT registry. The goal of this proposal is to collect clinical data from both FMT donors and recipients for the following purposes: 1) To assess short- and long-term safety; 2) to gather information on practice in the U.S. and assess effectiveness of the intervention; 3) to promote scientific investigation; and 4) to aid practitioners and trial sponsors in satisfying regulatory requirements. This registry will prospectively enroll patients who undergo FMT at sites throughout the U.S. Information on FMT methodology, FMT indication, as well as baseline data on donors and recipients will be collected from each site. Patients will be followed at regular intervals for up to 10 years after FMT for pre-defined and spontaneously reported adverse events and for pre-defined outcomes of effectiveness. The registry will facilitate statistical analyses for signal detection, generation of descriptive data, and the conduct of comparative effectiveness studies. A prospective cohort of 4,000 FMT patients will provide precise estimates of the incidence of safety and effectiveness endpoints in real-world practice and rule out uncommon adverse events with high confidence. This registry will link to an independent biobank that will collect, archive, and analyze approximately 3,000 fecal samples from the donors as well as recipients, providing a rich source for studying manipulation of the gut microbiota in humans. The leadership of the American Gastroenterological Association (AGA) and its partner organizations have worked together to develop the plans for this registry, which will be an extremely important tool to assess short-term safety, identify potential long-term consequences, determine effectiveness in real-world practice, help standardize best FMT practice, and gauge the potential consequences of manipulating the gut microbiome in human health and disease.